Yesterday, I was excitedly following the NASA press conference about the exoplanets found orbiting the star TRAPPIST-1 located 39 light years from earth. When I heard the day before that they’re going to announce something, the first idea that came to my mind was that they must have observed a combination of organic molecules and oxygen in some distant planet’s atmosphere, which would be a chemical nonequilibrium state that is difficult to explain without some kind of biology being present. Yes, of course you can’t have an atmosphere where there’s something like a mixture of methane and oxygen that is within flammability limits, but even very small concentrations of hydrocarbons and other organic compounds are apparently possible to notice from the IR spectrum of a distant object.
Actually, they didn’t have any spectral data yet, which could be used to make conclusions about the chemical composition of the atmospheres (that will be obtained later), but they had information about the masses, orbit radii and cross-sectional areas of the planets (these can be deduced from the oscillation of the star’s apparent position, see link “reduced mass“, and from the dimming of the light of the star when a planet temporarily moves past it), and the planet densities were too large for them to be gas-planets. Also, the temperatures of three of them seemed to be in the range where water can exist as a liquid at reasonable pressures.
Actually, a planet doesn’t necessarily need to even be in the so called habitable zone to possibly have liquid water – even on Mercury, the hottest planet on our Solar system, there are places that are always in shadow and can actually get quite cold because the rate of heat conduction through large masses of rock is slow compared to the rate of radiative heat loss to space. Therefore liquid water could exist in such places if contained inside some kind of “pocket” that would also protect it from low pressures. Also, the icy surface of Jupiter’s moon Europa can hide liquid water beneath it, because the tidal forces from Jupiter cause viscous (frictional) heating inside the moon, despite it being way too far from the Sun to be inside the definition of “habitable zone“.
So, more interesting stuff is probably coming, as the astronomers obtain infrared spectra from that star system.
Also, see the related discussion in Physics Forums here.
The featured image is from Wikimedia Commons.